/* ====================================================================
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2004 The Apache Software Foundation.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Apache" and "Apache Software Foundation" and
 *    "Apache Lucene" must not be used to endorse or promote products
 *    derived from this software without prior written permission. For
 *    written permission, please contact apache@apache.org.
 *
 * 5. Products derived from this software may not be called "Apache",
 *    "Apache Lucene", nor may "Apache" appear in their name, without
 *    prior written permission of the Apache Software Foundation.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 * $Id: FastCharStream.java,v 1.2 2004/10/30 09:58:25 lhelper Exp $
 */

package org.apache.lucene.queryParser;

import java.io.IOException;
import java.io.Reader;

/**
 * An efficient implementation of JavaCC's CharStream interface.
 * 
 * <p>
 * Note that this does not do line-number counting, but instead keeps track of
 * the character position of the token in the input, as required by Lucene's
 * {@link org.apache.lucene.analysis.Token} API.
 * </p>
 */
public final class FastCharStream implements CharStream {
	// ~ Instance fields
	// --------------------------------------------------------

	/** DOCUMENT ME! */
	char[] buffer = null;

	/** DOCUMENT ME! */
	int bufferLength = 0; // end of valid chars

	/** DOCUMENT ME! */
	int bufferPosition = 0; // next char to read

	/** DOCUMENT ME! */
	int tokenStart = 0; // offset in buffer

	/** DOCUMENT ME! */
	int bufferStart = 0; // position in file of buffer

	/** DOCUMENT ME! */
	Reader input; // source of chars

	// ~ Constructors
	// -----------------------------------------------------------

	/**
	 * Constructs from a Reader.
	 * 
	 * @param r
	 *            DOCUMENT ME!
	 */
	public FastCharStream(Reader r) {
		input = r;
	}

	// ~ Methods
	// ----------------------------------------------------------------

	/**
	 * DOCUMENT ME!
	 * 
	 * @return DOCUMENT ME!
	 * 
	 * @throws IOException
	 *             DOCUMENT ME!
	 */
	public final char readChar() throws IOException {
		if (bufferPosition >= bufferLength) {
			refill();
		}

		return buffer[bufferPosition++];
	}

	/**
	 * DOCUMENT ME!
	 * 
	 * @throws IOException
	 *             DOCUMENT ME!
	 */
	private final void refill() throws IOException {
		int newPosition = bufferLength - tokenStart;

		if (tokenStart == 0) { // token won't fit in buffer

			if (buffer == null) { // first time: alloc buffer
				buffer = new char[2048];
			} else if (bufferLength == buffer.length) { // grow buffer

				char[] newBuffer = new char[buffer.length * 2];
				System.arraycopy(buffer, 0, newBuffer, 0, bufferLength);
				buffer = newBuffer;
			}
		} else { // shift token to front
			System.arraycopy(buffer, tokenStart, buffer, 0, newPosition);
		}

		bufferLength = newPosition; // update state
		bufferPosition = newPosition;
		bufferStart += tokenStart;
		tokenStart = 0;

		int charsRead = input.read(buffer, newPosition, buffer.length - newPosition);

		if (charsRead == -1) {
			throw new IOException("read past eof");
		} else {
			bufferLength += charsRead;
		}
	}

	/**
	 * DOCUMENT ME!
	 * 
	 * @return DOCUMENT ME!
	 * 
	 * @throws IOException
	 *             DOCUMENT ME!
	 */
	public final char BeginToken() throws IOException {
		tokenStart = bufferPosition;

		return readChar();
	}

	/**
	 * DOCUMENT ME!
	 * 
	 * @param amount
	 *            DOCUMENT ME!
	 */
	public final void backup(int amount) {
		bufferPosition -= amount;
	}

	/**
	 * DOCUMENT ME!
	 * 
	 * @return DOCUMENT ME!
	 */
	public final String GetImage() {
		return new String(buffer, tokenStart, bufferPosition - tokenStart);
	}

	/**
	 * DOCUMENT ME!
	 * 
	 * @param len
	 *            DOCUMENT ME!
	 * 
	 * @return DOCUMENT ME!
	 */
	public final char[] GetSuffix(int len) {
		char[] value = new char[len];
		System.arraycopy(buffer, bufferPosition - len, value, 0, len);

		return value;
	}

	/**
	 * DOCUMENT ME!
	 */
	public final void Done() {
		try {
			input.close();
		} catch (IOException e) {
			System.err.println("Caught: " + e + "; ignoring.");
		}
	}

	/**
	 * DOCUMENT ME!
	 * 
	 * @return DOCUMENT ME!
	 */
	public final int getColumn() {
		return bufferStart + bufferPosition;
	}

	/**
	 * DOCUMENT ME!
	 * 
	 * @return DOCUMENT ME!
	 */
	public final int getLine() {
		return 1;
	}

	/**
	 * DOCUMENT ME!
	 * 
	 * @return DOCUMENT ME!
	 */
	public final int getEndColumn() {
		return bufferStart + bufferPosition;
	}

	/**
	 * DOCUMENT ME!
	 * 
	 * @return DOCUMENT ME!
	 */
	public final int getEndLine() {
		return 1;
	}

	/**
	 * DOCUMENT ME!
	 * 
	 * @return DOCUMENT ME!
	 */
	public final int getBeginColumn() {
		return bufferStart + tokenStart;
	}

	/**
	 * DOCUMENT ME!
	 * 
	 * @return DOCUMENT ME!
	 */
	public final int getBeginLine() {
		return 1;
	}
}
